High-temperature-resistant hydrophobic aerogel as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of high-temperature-resistant hydrophobic aerogel. The preparation method comprises the following preparation steps: (1) adding acid into a mixed solution of organic estersil or organic silicon and alcohol, controlling the pH value to 2-5.5, then adding silica sol, and stirring to obtain hydrolysate A; wherein the silica sol is a mixture of first silica sol with the D50 particle size of 8-20 nm and second silica sol with the D50 particle size of 50-100 nm; (2) adding a basic catalyst into the hydrolysate to obtain a sol substance B; (3) adding an opacifying agent and a flame retardant into the sol substance B to obtain a sol substance C; and (4) carrying out gelation, aging, hydrophobic modification and drying on the sol C to prepare the aerogel. The aerogel provided by the invention has excellent hydrophobic performance and extremely low water absorption rate at high temperature.

Description

Technical Field

[0001] This invention belongs to the technical field of aerogels, and more specifically, relates to a high-temperature resistant hydrophobic aerogel, its preparation method, and its application. Background Technology

[0002] Aerogels are ultralight, porous, solid materials with extremely high porosity, primarily filled with gas. They are typically produced by supercritical drying of gels, preserving the gel's three-dimensional network structure while removing the liquid components, hence the name aerogel. Existing aerogel preparation processes generally include: sol-gel reaction: hydrolysis and condensation of silanolates (such as TEOS) to form a wet gel; aging: hydrophobication; and supercritical drying.

[0003] Aerogel products on the market can only maintain hydrophobicity up to about 280℃. For high-temperature applications such as aerospace and petrochemical pipelines, where the long-term operating temperature is 300-400℃, especially in environmental contact and high-temperature construction scenarios, maintaining hydrophobicity above 300℃ is very important.

[0004] Currently, domestic methods to improve the hydrophobic temperature of aerogels involve special processing techniques: ① Modification with long-chain silanes (such as fluorosilanes). These silanes are very expensive, and long-chain silanes increase the carbon content of the aerogel, leading to a decrease in flame retardancy; ② High-temperature heat treatment (e.g., 400-500℃) to remove organic residues before hydrophobic modification. This method increases production steps, and the high-temperature treatment followed by modification increases the thermal conductivity of the product. Patent publication number CN115806427A discloses a low-cost method for preparing aerogels, which involves uniformly stirring an alcohol solvent, deionized water, a catalyst, and a silicon source to obtain sol A; uniformly mixing the alcohol solvent and silica sol to obtain sol B; mixing sol A and B to form a gel, aging, and drying to obtain the aerogel. However, the hydrophobic properties of aerogels prepared by the above methods still fail to meet practical application requirements at high temperatures. Therefore, how to better improve the hydrophobic properties of aerogels and enhance their hydrophobic performance at high temperatures has become an urgent technical problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, the primary objective of this invention is to provide a method for preparing a high-temperature resistant hydrophobic aerogel. The prepared aerogel exhibits excellent hydrophobic properties and extremely low water absorption at high temperatures, and also possesses a low thermal conductivity and good flame-retardant properties.

[0006] The second objective of this invention is to provide a high-temperature resistant hydrophobic aerogel prepared by the above-described preparation method.

[0007] The third objective of this invention is to provide an application of a high-temperature resistant, hydrophobic aerogel in the aerospace and petrochemical fields.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention claims protection for a method for preparing a high-temperature resistant, hydrophobic aerogel, comprising the following preparation steps: (1) Add acid to the organosilicon ester or a mixture of organosilicon and alcohol, control the pH to 2-5.5, then add silica sol, stir, and obtain hydrolysate A; wherein the silica sol is a mixture of a first silica sol with a D50 particle size of 8-20nm and a second silica sol with a D50 particle size of 50-100nm; (2) Add an alkaline catalyst to hydrolysate A and mix well to obtain sol B; (3) Add a light-blocking agent and a flame retardant to sol B, mix well, and obtain sol C; (4) Sol C is gelled to obtain wet gel; after aging, the wet gel is hydrophobically modified and dried to prepare a high-temperature resistant hydrophobic aerogel.

[0009] In this invention, by increasing the hydroxyl content in the system during the sol-gel stage, the bonding strength and number of hydrophobic groups in the modified product are enhanced. Using conventional modifiers, hydrophobic properties, including those at high temperatures, can be improved without affecting other product properties or increasing costs. Specifically: This invention incorporates a first silica sol and a second silica sol with different D50 particle sizes during the sol-gel stage. The first silica sol, with a D50 particle size of 8-20 nm, acts to cut the gel pores, resulting in a smaller and more uniform pore size in the aerogel, which is beneficial for the uniform distribution of subsequent light-blocking agents and flame retardants. The second silica sol, with a D50 particle size of 50-100 nm, provides more active hydroxyl sites, resulting in a more complete modification process and improved hydrophobic stability at high temperatures. Furthermore, the silica sol itself is a completely hydrolyzed inorganic silicon precursor without introducing organic groups. It can induce complete hydrolysis of organosilicon precursors, providing more modification sites for the system.

[0010] In step (1) of this invention, it is necessary to adjust the pH to 2-5.5, which is crucial because silica sol itself is aqueous. Adding it to the alcohol system will destroy hydration and the double electric layer structure on the particle surface, causing silica particles to precipitate. Under acidic conditions, the particle surface has a strong charge, the potential increases, and the van der Waals force and electrostatic repulsion are in balance, ensuring that the silica sol remains stably dispersed in the alcohol system.

[0011] Furthermore, this invention incorporates a light-blocking agent and a flame retardant in the sol-gel stage, which, when combined with the silica sol, exhibit excellent synergistic effects, maximizing the hydrophobic properties of the product at high temperatures. The combination of the light-blocking agent and the flame retardant also synergistically enhances the hydrophobic effect. Through the complementary "radiation protection" mechanism of the light-blocking agent and the "anti-conduction" mechanism of the flame retardant, the effect significantly surpasses that of a single additive. On one hand, both the light-blocking agent and the flame retardant can provide hydroxyl sites, helping to increase the number of hydrophobic groups; on the other hand, hydrophobic groups (such as -OCH3) are highly sensitive to radiation. The light-blocking agent and the flame retardant can reduce radiative heat transfer at high temperatures, effectively reducing chain scission of hydrophobic groups and improving their stability at high temperatures.

[0012] This invention does not use long-chain organosilane modifiers (such as fluorosilanes or benzene-containing silanes), resulting in low organic residue in the recycled alcohol system, simplified subsequent treatment processes, and reduced emissions of waste gas, wastewater, and solid waste. This invention eliminates the need for drying followed by high-temperature heat treatment, saving energy and reducing the burden on waste gas treatment by eliminating additional VOC emissions.

[0013] Preferably, in step (1), the pH needs to be adjusted to 2-4. Under these preferred conditions, the prepared aerogel has superior hydrophobic properties. More specifically, in step (1), the pH can be adjusted to 2.3, 2.5, 2.8, 3.3, 3.5, 3.8, or any range formed by the above values; the present invention is not limited thereto.

[0014] Preferably, in step (1), the mass ratio of the first silica sol and the second silica sol is 1:1-5; and / or The concentrations of the first and second silica sols are 30-50%; and / or The silica sol is a mixture of a first silica sol with a D50 particle size of 10-15 nm and a second silica sol with a D50 particle size of 60-90 nm.

[0015] Specifically, the D50 particle size of the first silica sol is 10-12 nm. More specifically, the D50 particle size of the first silica sol can be 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, etc., or any range formed by the above values, such as 10-15 nm, 10-12 nm, 8-18 nm, etc., and the present invention is not limited thereto.

[0016] Specifically, the D50 particle size of the second silica sol is 75-85 nm. More specifically, the D50 particle size of the second silica sol can be 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, etc., or any range formed by the above values, such as 50-90 nm, 70-80 nm, 75-95 nm, etc., and the present invention is not limited thereto.

[0017] Preferably, the silica sol is prepared by using water glass as a raw material and preparing it via ion exchange. More specifically, in some embodiments, the silica sol is prepared by using water glass through a strongly acidic cation exchange resin, followed by aging and concentration to obtain the silica sol.

[0018] Preferably, the silica sol is used within 7 days of its preparation. By using homemade silica sol, the silica sol can be directly involved in the preparation of silica, maximizing the retention of the hydroxyl activity on the silica sol surface and avoiding the influence of various stabilizers added to commercially available silica sol on the stability and reactivity of the silica sol system.

[0019] Preferably, the mass ratio of organosilicon ester or organosilicon, alcohol, silica sol, water, acid and basic catalyst is 1:(4-12):(0.1-0.4):(0.3-0.8):(0.005-0.05):(0.01-0.1). Preferably, the mass ratio of organosilicon ester or organosilicon, alcohol, silica sol, water, acid and basic catalyst is 1:(6-8):(0.1-0.2):(0.4-0.6):(0.02-0.04):(0.02-0.06).

[0020] Preferably, the organosilicon ester is selected from at least one of tetraethyl orthosilicate, methyl orthosilicate, and polysilicate; the organosilicon is selected from at least one of methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, propyltrimethoxysilane, and propyltriethoxysilane.

[0021] Preferably, the alcohol is at least one selected from ethanol, methanol, isopropanol, and butanol.

[0022] Preferably, the acid is at least one of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, acetic acid, and oxalic acid. More specifically, the concentration of the acid is 0.1-1 mol / L.

[0023] Preferably, the alkaline catalyst is selected from at least one of ammonia, ammonium fluoride, sodium bicarbonate, ammonium bicarbonate, ethanolamine, lithium hydroxide, sodium hydroxide, triethylamine, urea, and γ-aminopropyltriethoxysilane (KH550). More specifically, the concentration of the alkaline catalyst is 0.1-2 mol / L.

[0024] Preferably, the light-blocking agent is selected from at least one of silicon carbide, titanium dioxide, titanium nickel yellow, iron chromium black, zinc barium white, and carbon black.

[0025] Preferably, the light-blocking agent is a mixture of titanium dioxide, titanium nickel yellow, and iron chromium black; more preferably, the mass ratio of titanium dioxide, titanium nickel yellow, and iron chromium black is 1:1:1-3. Titanium dioxide has strong scattering of ultraviolet light but weak infrared absorption. Titanium nickel yellow can complement the shortcomings of titanium dioxide, especially with strong absorption of near-infrared light in the 800-1300nm range. Iron chromium black has strong absorption of ultraviolet light. The inventors have found through research that when the above-mentioned light-blocking agents are combined, the chain scission of hydrophobic groups in the aerogel can be greatly reduced, and the stability of hydrophobic groups at high temperatures can be improved, which is better than using a single light-blocking agent.

[0026] Preferably, the D50 particle size of the light-blocking agent is 1-5 μm. Specifically, the D50 particle size of the light-blocking agent can be 1.3 μm, 1.5 μm, 1.8 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3.3 μm, 3.5 μm, 3.8 μm, 4.3 μm, 4.5 μm, 4.8 μm, etc., or any range formed by the above values, such as 1.3-3.5 μm, 2.5-4.5 μm, etc., and the present invention is not limited thereto. If the particle size of the light-blocking agent is too large, uneven dispersion will occur during the preparation process, and it will easily settle; while if the particle size of the light-blocking agent is too small, it will block the pores of the aerogel itself, affecting its hydrophobic properties. Therefore, within the above-mentioned preferred particle size range, the prepared aerogel can better improve the hydrophobic properties and the hydrophobic properties at high temperatures.

[0027] Preferably, the flame retardant is selected from at least one of magnesium oxide, magnesium hydroxide, aluminum hydroxide, ammonium polyphosphate, zinc borate, montmorillonite, and calcium carbonate.

[0028] Preferably, the flame retardant is a mixture of magnesium oxide and magnesium hydroxide; more preferably, the mass ratio of magnesium oxide to magnesium hydroxide is 1:1-5. More preferably, the mass ratio of magnesium oxide to magnesium hydroxide is 1:1-3. Using a combination of magnesium hydroxide and magnesium oxide achieves a perfect blend of flame retardant properties. Magnesium hydroxide decomposes upon heating, producing water vapor, reducing stability, diluting the oxygen concentration, and forming a magnesium oxide barrier layer. This layer, together with magnesium oxide, forms a dense ceramic layer that blocks oxygen, improving flame retardant performance while preventing the oxidative decomposition of hydrophobic groups. This increases the hydrophobic failure temperature of the aerogel, thereby improving its hydrophobic properties at high temperatures, and the effect is superior to using a single opacifier.

[0029] Preferably, the D50 particle size of the flame retardant is 0.1-3 μm. Preferably, the D50 particle size of the flame retardant is 0.3-1 μm. Preferably, the D50 particle size of the flame retardant is 0.3-0.5 μm. Specifically, the D50 particle size of the flame retardant can be 0.3 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.3 μm, 1.8 μm, 2.3 μm, 2.5 μm, 2.8 μm, etc., or any range formed by the above values, such as 0.3-0.5 μm, 0.3-1.5 μm, etc., and the present invention is not limited thereto. If the D50 particle size of the flame retardant is too large, uneven dispersion will occur during the preparation process, and it will easily settle; while if the D50 particle size of the flame retardant is too small, it will block the pores of the aerogel itself, affecting its hydrophobic properties. Therefore, within the above-mentioned preferred D50 particle size range, the prepared aerogel can better improve hydrophobic properties and hydrophobic properties at high temperatures.

[0030] Preferably, the total amount of opaque agent added is 0.5-3% of the total mass of sol C.

[0031] Preferably, the total amount of flame retardant added is 1-2% of the total mass of the sol C.

[0032] Preferably, in step (4), the gelation operation is as follows: pour the sol C into a mold or impregnate the fiber felt, wait for gelation, and then obtain a wet gel or a wet gel product.

[0033] Specifically, the fiber felt is selected from at least one of glass fiber felt, ceramic fiber felt, basalt fiber felt, pre-oxidized fiber felt, polyimide fiber felt, PET fiber felt, and melamine foam.

[0034] Preferably, in step (4), the aging process is carried out for 4-12 hours under sealed, room temperature and static conditions.

[0035] Preferably, in step (4), a modifying liquid containing a silane coupling agent is used to perform hydrophobic modification on the wet gel.

[0036] Preferably, in step (4), the volume ratio of wet gel to modified liquid is 1:1-1.5.

[0037] Preferably, in some specific embodiments, the wet gel can be soaked in the modified liquid for 4-12 hours.

[0038] Preferably, the modified liquid is a mixture of alcohol and modifier. The mass ratio of alcohol to modifier is 85-95:5-15.

[0039] Preferably, the modifier is selected from at least one of hexamethyldisilazane, hexamethyldisiloxane, trimethylchlorosilane, dimethyldimethoxysilane, dimethyldiethoxysilane, and propyltrimethoxysilane.

[0040] Preferably, the drying is performed using a supercritical process. More specifically, the drying is performed using supercritical carbon dioxide drying.

[0041] Specifically, the drying process of the supercritical carbon dioxide is as follows: the material to be dried is placed in a drying kettle, the carbon dioxide is cooled into a liquid state, pressurized to 12-20 MPa by a high-pressure pump, heated to 40-70°C, and enters the drying kettle in a supercritical state. When the pressure in the drying kettle rises to 12-18 MPa and the temperature rises to 40-70°C, the temperature and pressure are maintained for 2-5 hours. After gas-liquid separation in a separation kettle, a high-temperature resistant and hydrophobic aerogel is obtained.

[0042] Furthermore, this invention seeks protection for the high-temperature resistant hydrophobic aerogel prepared by the above preparation method.

[0043] Furthermore, this invention seeks to protect the application of the above-mentioned high-temperature resistant and hydrophobic aerogel in the aerospace and petrochemical fields.

[0044] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a high-temperature resistant hydrophobic aerogel. By employing silica sols with different particle size combinations in the sol-gel stage, along with a light-blocking agent and a flame retardant, an excellent synergistic effect is achieved. On the one hand, this significantly increases the hydroxyl content in the system, thereby improving the number and bonding strength of hydrophobic groups in the modified aerogel. On the other hand, the light-blocking agent and flame retardant, while providing hydroxyl groups, weaken the radiation effects at high temperatures, enhancing the hydrophobic stability of the hydrophobic groups at high temperatures. The aerogel prepared by this invention, while maintaining a low thermal conductivity and good flame retardant properties, exhibits excellent hydrophobic properties and extremely low water absorption at 350℃. Detailed Implementation

[0045] The present invention will be further described below with reference to the specification and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0046] Silica sol 1, with a D50 particle size of 10 nm and a mass concentration of 40%, was prepared in-house. The preparation method was as follows: water glass (modulus 3.5, concentration 40%) was diluted to a concentration of 20%, filtered, and passed through a strongly acidic styrene cation exchange resin (model 732) to generate silica sol particles. The mixture was then aged at 65℃ for 1.5 h, and concentrated by heating at 80-90℃ for 12 h to obtain the self-made silica sol.

[0047] Silica sol 2, with a D50 particle size of 80 nm and a mass concentration of 40%, was prepared in-house. The preparation method of silica sol 2 is the same as that of silica sol 1, except that it was cured at 85°C for 4 hours.

[0048] Opacifier 1, titanium dioxide, D50 particle size of 1μm, R930, Japanese Ishihara rutile titanium dioxide.

[0049] Opacifier 2, titanium nickel yellow, D50 particle size of 1.5μm, 13905, Suzhou Jingyan New Materials Co., Ltd.

[0050] Opacifier 3, iron chromium black, D50 particle size 1.5μm, A2901, Hubei Jufa Pigment Co., Ltd.

[0051] Opacity agent 4, titanium dioxide, D50 particle size of 0.25μm, CR57, Japanese Ishihara rutile titanium dioxide.

[0052] Flame retardant 1, magnesium hydroxide, D50 particle size is 0.5μm; YC-QM50, Shanghai Yingcheng New Materials Co., Ltd.

[0053] Flame retardant 2, magnesium oxide, D50 particle size is 0.3μm; YC-Mg300Y, Shanghai Yingcheng New Materials Co., Ltd.

[0054] Unless otherwise specified, all components used in the parallel embodiments and comparative examples are the same commercially available products.

[0055] Example 1: A high-temperature resistant and hydrophobic aerogel (1) Weigh 110g of methyl orthosilicate and 825g of methanol, stir for 10min at a stirring speed of 600 rpm. Add 4.2g of 0.5mol / L acetic acid solution and 55g of pure water, stir for 5min, adjust the pH of the solution to 3, add 5g of silica sol 1 and 10g of silica sol 2, and continue stirring for 25min to obtain hydrolysate A.

[0056] (2) Add 4.5 g of 1 mol / L ammonia solution to hydrolysate A, stir continuously for 10 min, adjust the pH of the solution to 7, and obtain sol B.

[0057] (3) Increase the rotation speed to 1000 rpm, add 2.5g of opaque agent 1, 2.5g of opaque agent 2, 5g of opaque agent 3, 10g of flame retardant 1, and 5g of flame retardant 2 to sol B, and continue stirring for 15 minutes to obtain sol C.

[0058] (4) Cut a glass fiber needle-punched felt with a length * width * thickness (300 * 300 * 10 mm) and put it into a mold. Immerse the fiber felt with sol B and seal it until it is completely soaked. Let it stand until it gels. The gel time is 30 min. After gelation, let it stand for 6 h to age and obtain the gel product.

[0059] (5) Prepare a modification solution by mass ratio of dimethyldimethoxysilane:methanol = 5:95. Weigh 45g of dimethyldimethoxysilane and 855g of methanol, and mix them evenly to obtain the modification solution. Place the gel product into the modification tank, add the modification solution (by volume ratio of gel product:modification solution = 1:1.2), control the temperature at 50℃, and circulate for modification for 5 hours to obtain the modified semi-finished product.

[0060] (6) The semi-finished product is placed in the drying kettle. The carbon dioxide is cooled into liquid state, pressurized to 15MPa by a high-pressure pump, heated to 65℃, and enters the drying kettle in a supercritical state. When the pressure of the drying kettle rises to 15MPa and the temperature rises to 60℃, it is circulated for 2 hours. After gas-liquid separation in the separation kettle, the separation kettle is used until no liquid flows out, and high-temperature resistant hydrophobic aerogel is obtained.

[0061] Example 2: A high-temperature resistant and hydrophobic aerogel The difference between this embodiment and embodiment 1 is that in step (3), 10g of light-blocking agent 1, 10g of flame retardant 1, and 5g of flame retardant 2 are added.

[0062] Example 3: A high-temperature resistant and hydrophobic aerogel The difference between this embodiment and embodiment 1 is that in step (3), 10g of light-blocking agent 2, 10g of flame retardant 1, and 5g of flame retardant 2 are added.

[0063] Example 4: A high-temperature resistant and hydrophobic aerogel The difference between this embodiment and embodiment 1 is that in step (3), 10g of light-blocking agent 3, 10g of flame retardant 1, and 5g of flame retardant 2 are added.

[0064] Example 5: A high-temperature resistant and hydrophobic aerogel The difference between this embodiment and embodiment 1 is that in step (3), 10g of light-blocking agent 4, 10g of flame retardant 1, and 5g of flame retardant 2 are added.

[0065] Example 6: A high-temperature resistant and hydrophobic aerogel The difference between this embodiment and embodiment 1 is that in step (3), 2.5g of opaque agent 1, 2.5g of opaque agent 2, 5g of opaque agent 3, and 15g of flame retardant 1 are added.

[0066] Example 7: A high-temperature resistant and hydrophobic aerogel The difference between this embodiment and embodiment 1 is that in step (3), 2.5g of opaque agent 1, 2.5g of opaque agent 2, 5g of opaque agent 3, and 15g of flame retardant 2 are added.

[0067] Example 8: A high-temperature resistant and hydrophobic aerogel The difference between this embodiment and embodiment 1 is that in step (1), the pH of the solution is adjusted to 5.5.

[0068] Comparative Example 1: A heat-resistant and hydrophobic aerogel The difference between this comparative example and Example 1 is as follows: in step (1), silica sol was not added; in step (3), light-shielding agent and flame retardant were not added.

[0069] Comparative Example 2: A heat-resistant and hydrophobic aerogel The difference between this comparative example and Example 1 is as follows: in step (1), silica sol was not added.

[0070] Comparative Example 3: A heat-resistant and hydrophobic aerogel The difference between this comparative example and Example 1 is as follows: in step (3), light-shielding agent and flame retardant were not added.

[0071] Comparative Example 4: A heat-resistant and hydrophobic aerogel The difference between this comparative example and Example 1 is as follows: in step (3), light-shielding agent was not added.

[0072] Comparative Example 5: A heat-resistant and hydrophobic aerogel The difference between this comparative example and Example 1 is as follows: in step (3), flame retardant was not added.

[0073] Comparative Example 6: A heat-resistant and hydrophobic aerogel The difference between this comparative example and Example 1 is as follows: in step (1), 15 g of silica sol 2 was added instead of silica sol 1.

[0074] Comparative Example 7: A heat-resistant and hydrophobic aerogel The difference between this comparative example and Example 1 is as follows: in step (1), 15 g of silica sol 1 was added instead of silica sol 2.

[0075] Test Example The heat-resistant and hydrophobic aerogels obtained in the above examples and comparative examples were tested as follows.

[0076] (1) Heat (350 °C) hydrophobicity test: The hydrophobicity rate was detected according to GB / T 10299-2011, and the hydrophobicity rate of the aerogel product ≥ 98% was qualified. The specific detection method and results: Step 1: Cut a sample 1-1 with length * width * thickness = 30 * 15 * 0.1 cm, place it in an oven for heat treatment at 125 °C for 2 h until constant weight, weigh the mass M1, fix the treated sample on a shelf at a 45° angle to the horizontal plane, turn on the water source, and spray water on the sample at a flow rate of 10 ml / s. Stop spraying after 1 h, weigh the mass M2, and calculate according to formula (1) to obtain the hydrophobicity rate; Step 2: Place the sample 1-1 in a muffle furnace, heat it to 350 °C, start timing, keep it at a constant temperature for 24 h, cool it to below 100 °C, and take out the sample to obtain sample 1-2; Step 3: Repeat step 1, weigh samples 1-2 (M1 and M2), and calculate the hydrophobicity according to formula (1).

[0077] Hydrophobicity = (1 - (M2 - M1) / M1) * 100%; In formula (1), M1 is the mass of the sample before spraying and M2 is the mass of the sample after spraying.

[0078] The high-temperature (260℃) hydrophobicity test and the high-temperature (280℃) hydrophobicity test are the same as the above test methods, except that in step two, the temperature is heated to 260℃ and 280℃ respectively.

[0079] (2) Test method for water absorption rate: The test shall be conducted in accordance with GB / T 5480-2017, using the full immersion mass water absorption rate test method.

[0080] (3) Thermal conductivity: The thermal conductivity of the aerogel was tested using a thermal conductivity meter (Netzsch HFM446Lambda M model) according to the national standard GB / T 10295 heat flow meter method.

[0081] (4) Flame retardant performance: The flame retardant performance was tested according to the national standard GB8624-2012 "Classification of Combustion Performance of Building Materials and Products" using a fully automatic calorimeter (Henan Hebi Tianke Instrument Co., Ltd., ZDHW-8A type).

[0082] Tables 1 and 2 show the test data for the high-temperature resistant hydrophobic aerogels prepared in the examples and comparative examples, respectively.

[0083] Table 1

[0084] Table 2

[0085] As can be seen from the above, the high-temperature resistant hydrophobic aerogel provided by the present invention has excellent hydrophobicity and hydrophobic properties at high temperatures. Furthermore, the aerogel provided by the present invention also has excellent thermal conductivity and flame retardant properties. More specifically, after treatment at 260℃, the aerogel has a hydrophobicity ≥99% and a water absorption rate ≤1%; after treatment at 280℃, the hydrophobicity ≥97% and the water absorption rate ≤3%; after treatment at 350℃, the hydrophobicity ≥91.6% and the water absorption rate ≤8.4%; and the thermal conductivity ≤0.0191 and the flame retardant performance ≤A2 level. Preferably, after treatment at 350℃, the hydrophobicity ≥96.2% and the water absorption rate ≤3.8%; preferably, after treatment at 350℃, the hydrophobicity ≥99.2% and the water absorption rate ≤0.8%.

[0086] As can be seen from Examples 1 and 2-4, when a composite opaque agent is used, the prepared aerogel has better hydrophobic properties.

[0087] As can be seen from Examples 1 and 5, when the D50 particle size of the opacifier is within a specific range, the prepared aerogel has better hydrophobic properties.

[0088] As can be seen from Examples 1 and 6-7, when a composite flame retardant is used, the prepared aerogel has better hydrophobic and flame retardant properties.

[0089] As can be seen from Examples 1 and 8, when the pH of step (1) is 2-4, the prepared aerogel has better hydrophobic properties.

[0090] As can be seen from Examples 1 and Comparative Examples 1-3, it is difficult to achieve the technical effects of the present invention without adding silica sol, or without adding light-blocking agents and flame retardants during the preparation process; and the water absorption rate of the aerogels prepared in Comparative Examples 1-3 increased significantly after heat treatment at 350℃. As can be seen from Examples 1 and Comparative Examples 1-3, the present invention, by using silica sol in combination with light-blocking agents and flame retardants, achieves excellent synergistic improvement in the hydrophobic properties of aerogels and their hydrophobic properties at high temperatures.

[0091] As can be seen from Examples 1, 2, and 4-5, the combination of light-blocking agents and flame retardants in this invention can achieve excellent synergistic effects, thereby improving the hydrophobic properties of the aerogel.

[0092] As can be seen from Examples 1 and Comparative Examples 6-7, the technical effects of the present invention can only be achieved when a combination of a first silica sol with a specific D50 particle size and a second silica sol with a specific D50 particle size is used.

[0093] The foregoing examples are merely illustrative, used to explain some features of the method described in this invention. The appended claims are intended to claim the broadest possible scope, and the embodiments presented herein are demonstrated by the applicant's actual experimental results. Therefore, the applicant intends that the appended claims are not limited by the selection of examples illustrating the features of the invention. Some numerical ranges used in the claims also include sub-ranges within them, and variations within these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A method for preparing a high-temperature resistant, hydrophobic aerogel, characterized in that, The preparation steps include the following: (1) Add acid to the organosilicon ester or a mixture of organosilicon and alcohol, control the pH to 2-5.5, then add silica sol, stir, and obtain hydrolysate A; wherein the silica sol is a mixture of a first silica sol with a D50 particle size of 8-20nm and a second silica sol with a D50 particle size of 50-100nm; (2) Add an alkaline catalyst to hydrolysate A and mix well to obtain sol B; (3) Add a light-blocking agent and a flame retardant to sol B, mix well, and obtain sol C; (4) Sol C is gelled to obtain wet gel; after aging, the wet gel is hydrophobically modified and dried to prepare a high-temperature resistant hydrophobic aerogel.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the first silica sol to the second silica sol is 1:1-5; and / or The concentrations of the first and second silica sols are 30-50%; and / or The silica sol is a mixture of a first silica sol with a D50 particle size of 10-15 nm and a second silica sol with a D50 particle size of 60-90 nm.

3. The preparation method according to claim 1, characterized in that, The silica sol is prepared using water glass as a raw material via ion exchange.

4. The preparation method according to claim 1, characterized in that, The light-blocking agent is selected from at least one of silicon carbide, titanium dioxide, titanium nickel yellow, iron chromium black, zinc barium white, and carbon black; Preferably, the opacifier is a mixture of titanium dioxide, titanium nickel yellow, and iron chromium black; more preferably, the mass ratio of titanium dioxide, titanium nickel yellow, and iron chromium black is 1:1:1-3.

5. The preparation method according to claim 1 or 4, characterized in that, The D50 particle size of the opaque agent is 1-5 μm.

6. The preparation method according to claim 1 or 4, characterized in that, The flame retardant is selected from at least one of magnesium oxide, magnesium hydroxide, aluminum hydroxide, ammonium polyphosphate, zinc borate, montmorillonite, and calcium carbonate; Preferably, the flame retardant is a mixture of magnesium oxide and magnesium hydroxide; more preferably, the mass ratio of magnesium oxide to magnesium hydroxide is 1:1-5.

7. The preparation method according to claim 1, characterized in that, The flame retardant has a D50 particle size of 0.1-3 μm.

8. The preparation method according to claim 1, characterized in that, In step (4), a modifying liquid containing a silane coupling agent is used to perform hydrophobic modification on the wet gel.

9. The high-temperature resistant hydrophobic aerogel prepared by the preparation method according to any one of claims 1-8.

10. The application of the high-temperature resistant hydrophobic aerogel of claim 9 in the aerospace and petrochemical fields.

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